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> Imagine you are debugging a 10000 line function that's suppose to return an int, but instead returns a NaN.

I'm imagining that. It's my first day at a new job cleaning up a legacy codebase, but upon opening up a single 10kloc function written in JS, I realize that I made a terrible mistake and immediately hand in my resignation.

In the meantime, I set a breakpoint at the end of the function, inspect the inline value annotations for NaNs, and trace them back to the start.

Relative to any other debugging task in a 10kloc function, that doesn't sound bad at all. If it's consistently returning NaN, that should take maybe half an hour.

Also, I'd be really surprised if the function was made to return an int, because JS doesn't have integer datatypes.

Read what I wrote again:

> Sure, I can say all kinds of stuff to make finding this error sound simple but if exceptions were thrown instead of assigning NaNs to some variable life would be easier.

I said this in the parent post and sure enough the reply is exactly inline with what I said was going to happen. I don't hate javascript, but it has its horrible horrible warts.

>Relative to any other debugging task in a 10kloc function, that doesn't sound bad at all. If it's consistently returning NaN, that should take maybe half an hour.

An exception would take a second. An exception would give you the target line of every illegal operation; while a NaN propagates itself like a virus along every arithmetic operation.

Some people find it easy to run a 20 miles, sure but that still doesn't change the fact that cars are much better. Get the analogy? You are running 20 miles and telling me how you don't mind... I'm saying sure, but driving still has a purpose in life.

> I said this in the parent post and sure enough someone who is a fan of javascript had to reply with exactly what I said was going to happen.

Breakpoints are off the table? Seriously? I didn't realizing using a debugger made me a JS fanboy.

Wrapping all of your basic arithmetic in try/catch blocks is completely unreasonable. If you need to check for NaN, check for NaN. Making arithmetic substantially slower in the general case to catch the uncommon cases is exactly the problem NaN was introduced to solve.

No dude. I'm not saying it's off the table. I'm saying it shouldn't be necessary for a 1/0 illegal operation.

I'm not even saying to wrap your functions in try catches. If your program has a 1/0 operation then obviously you made a mistake somewhere. With javascript you have to hunt that mistake down, with a language like python you get the line number of where that mistake occurred. The exception is there for the entire program to fail so that you can correct your mistake. The language should not allow operations to occur that create these things called NaNs and thus automatically this removes the need to check for NaNs too. That's all I'm saying.

BTW unless you explicitly instantiated a NaN you should rarely ever be checking for NaN's in your code. NaNs represent illegal operations like 1/0, and thus any type of code producing a NaN should be killed. If you check for NaNs in your code that means you are guarding your code from your own bugs.

>I didn't realizing using a debugger made me a JS fanboy.

Yeah that was inappropriate. I apologize for calling you that, unfortunately you still saw it before I edited it out.

Look, misattributing the introduction of NaN to JS is not going to help make the case that JS is poorly designed[1].

JS uses double-precision floating point numbers, based on the IEEE 754 standard first published in 1985.

[1]: Though there is a case that using doubles for all numbers is poor design, that's a different topic altogether.

I don't know where NaNs were introduced, but I never attributed the introduction of NaNs to javascript. If JS is just propagating a bad design, it still fits the description of being poorly designed.

Not to mention a null. null + 1 = 1. This is even worse. Your 1000loc function returns a legit number but it's a little bit off... and you have to find it. Imagine never having to have to do that with a language like python... 1+None and 1/0 all return named exceptions with line numbers in python.

No, not following the globally agreed upon standard for the sole purpose of making arithmetic slower in the general case would be bad design.

https://dzone.com/articles/the-worst-mistake-of-computer-sci...

Keep in mind this guy didn't even mention how javascript handles nulls. While nulls bypass typecheckers, typically a null + 1 throws an exception. Not so in javascript... null + 1 returns a 1 in javascript.

Null and NaN are different concepts with different trade-offs and different behavior when working with them. Nulls don't have special processor support[1] and are not part of a multilanguage, multiprocessor, international standard.

[1]: So far as I'm aware, though I'd love to read about it if I'm wrong.

what are you talking about? when did i say I want to make arithmetic slower? And how is that globally agreed upon as a standard? In math when you get a NaN, do mathematicians continue to use it as a variable or do they realize they made a mistake? Think about it. In all math and science It's actually globally agreed upon that a NaN is not a variable you can reuse in some other function.

> And how is that globally agreed upon as a standard?

Because all modern processors and mainstream languages implement their floating point calculations as IEEE 754.

> when did i say I want to make arithmetic slower?

When you said you wanted to introduce exceptions whenever NaN is encountered.

Your processor has instructions that add/subtract/divide/multiply floating point numbers according to the IEEE 754 standard. What you propose is to then check in the implementation of JS after each instruction to see if the result is NaN, which is going to be a speed reduction of at least 2-3x, though I would expect it to actually be higher than that because branching can get expensive. (Making a note to go try it and benchmark)

Then, after doing this check, you want to have JS throw an exception. This only slows down the uncommon case, so that's not much of an issue, but in situations where NaNs are able to be treated as valid values, they then have to catch these exceptions and resume normal execution flow.

The result is that there is a happy path slowdown of arithmetic operations by at least 2-3x, to gain an arguable advantage in debugging time in the unhappy path.

Throwing away compatibility with other languages and working against the processor are not goals I'd shoot for, and wrapping basic arithmetic in try/catch blocks doesn't sound like a very good payout for doing so.

>Throwing away compatibility with other languages and working against the processor are not goals I'd shoot for, and wrapping basic arithmetic in try/catch blocks doesn't sound like a very good payout for doing so.

Almost every popular language launches an exception when you do a divide by zero.

>Your processor has instructions that add/subtract/divide/multiply floating point numbers according to the IEEE 754 standard. What you propose is to then check in the implementation of JS after each instruction to see if the result is NaN, which is going to be a speed reduction of at least 2-3x, though I would expect it to actually be higher than that because branching can get expensive. (Making a note to go try it and benchmark)

Try it, I'd like to see the results. I'm not too familiar with the processor implementation, but something tells me that if every system level language implements exceptions for division by zero then the cost must be minimal. Also how would it be a 3x slow down? At most it's just one instruction.

Interestingly in some languages integer division by zero throws an exception and floating point division by zero returns some kind of infinite or NaN value.

If this behavior was propagated down from processor design, I'd say the processors made a bad choice. Why is this behavior specific to floating point? Why is the behavior for integers different. Either way when I say poorly designed, I mean poorly designed in terms of usability, not speed. Clearly, javascript wasn't initially designed for speed.

Like I said, the purpose of a division by zero exception is not to be caught. It's to prevent a buggy program from continuing to run. The only place a division by zero operation can legally occur is if the zero arrives via IO. In that case it's better to sanitize the input or detect the zero rather than catch an exception.